We recently went through something like this--had a 99 expedition that we had leased and my husband got an 01 S80 so that left me with the expedition & the 850. I went back and forth with doing a buy on the truck and also having the 850 (which we won't sell & was finally paid for at the same time the lease was up). After much thinking, I came to the conclusion that no car payments are better than one, the 850 runs great (182K), I hardly go anywhere, so what's the point of having two cars when one paid for one will do. The point is that since the 850 runs so well and we have probably done all the repairs on the common faults, why not use it till it dies? Besides, it was the first Volvo and my husbands first love we're not going to give it away. If yours is paid for and you've come this far mileage wise, I would just keep it for an extra for those just in case days.
That's just my two cents...................